Physical and mechanical properties and related microscopic characteristics of high-temperature granite after water-cooling

In order to understand the deterioration of physical and mechanical properties of high-temperature rocks, and the related microscopic characteristics after water-cooling during the thermal reservoir construction, uniaxial compression tests were conducted on five groups of granite samples, which at normal temperature and 200, 400, 600, and 800 degrees C had experienced water-cooling shocks, respectively. Ultrasonic testing, XRD and polarizing microscope observation were adopted to analyze the microscopic failure mechanics of rocks. Results show that with the increase of rock temperature, the peak strength decreases gradually with an increase of the peak strain, and the failure mode changes from sudden brittle failure to progressive failure. The mass loss rate, volume expansion rate, and density reduction rate increase with the increase of temperature, except for the ultrasonic wave velocity. The volume expansion rate of cooled rock samples increases significantly when the temperature ranges from 400 degrees C to 600 degrees C, and the attenuation rate of wave-velocity of rock samples decreases when the temperature ranges from 600 degrees C to 800 degrees C. It is found that the larger the temperature gradient, the more the transgranular cracks form due to the water-cooling shocks. A large number of transgranular and intergranular cracks cause the failure modes of rock samples under uniaxial compression to change from tension-shear failure to shear dominant failure accompanied by a large amount of powdery debris.